A math model that can describe the effect of stimulated Raman scattering (SRS) on a pilot-tone detection technique is developed. Through numerical simulation, it is shown that the effect of SRS could produce ghost tones. The power of the ghost tone is larger for the channels separated farther from the real tone. The experiment results show that this model can evaluate the effect accurately. The power ratio between real tone and ghost tone increases linearly with the increase of transmission length when wavelengths transmit longer than 300 km.